Microstructure and mechanical properties of multiprincipal component CoCrFeNiMox alloys

Four multiprincipal component CoCrFeNiMox (x = 0, 0.3, 0.5, and 0.85, in molar ratio) alloys were synthesized by vacuum arc-melting in a copper mould. The effects of variations in the amount of Mo on the microstructure and mechanical properties were investigated. The CoCrFeNi alloy exhibits a single face-centered cubic solid solution, whereas a (Cr,Mo)-rich σ phase is observed in the face-centered cubic matrix after the addition of Mo into the alloy. A (Mo,Cr)-rich μ phase appears on the fringes of the σ phase in the CoCrFeNiMo0.85 alloy. The hardness of face-centered cubic matrix and the σ-phase content increase with increasing Mo concentration, resulting in an increase in the alloy hardness, from HV135 to HV420. The compressive strength of the alloy improves as the Mo content increasing, but a simultaneous degradation of the ductility is observed. Accordingly, as the Mo content increases from 0 to 0.85, the yield stress and compressive strength rise from 136 MPa and 871 MPa to 929 MPa and 1441 MPa, respectively, and the fracture strain lowers from 75% to 21%. The solid-solution strengthening of the face-centered cubic matrix and the formation of the σ/or σ + μ phases are the two main reasons for the strengthening of the alloy.